RFID tags are beginning to enter the retail market on individual products. The presence of such tags on individual retail merchandise items offers a number of interesting possibilities for the retailer. In order to interact with an RFID tag (generally a small piece of silicon circuitry coupled to a small profile antenna) attached to merchandise, the RFID tag must usually be irradiated with an RF signal from an RFID tag reader. The RF signal then activates circuitry in the tag responsive to which the tag emits another RF signal which is in turn received by the tag reader, decoded, and transferred to a computer system for further processing consistent with the application. The signal from the tag will typically contain information describing the merchandise, e.g., price, size, type, brand, and the like. For example, in one application, one could place goods for sale on retail shelving, racks or hanger rods. Then, when the merchandise was removed from the immediate area where it was stored, this removal would be sensed and interactive sales information (e.g., coordinated outfits, different sizes, different designs, different colors, accessories, optional equipments and the like) could be displayed on a locally placed video display to encourage the buyer to buy additional merchandise related in some manner to the initial selection.
In order to transmit and receive signals the RFID reader requires its own antenna. While suitable for their intended purposes, known antennas for use in RFID applications are not suitable for covering a small defined volume such as a portion of a shelf, or the like, while being able to communicate with the tag placed in any orientation and being able to distinguish the absence of the tag from that small volume (in cooperation with suitable computational equipment).
FIG. 1 is a front perspective view of a prior art antenna assembly. In FIG. 1 a rectangular patch resonator is disposed above a conducting plane. It can be elongated as shown. This approach results in a single linear polarization (horizontal as shown in FIG. 1). The radiation is predominantly single-sided (directed upward in the FIG. 1 view). At least two conductor layers are required to feed this antenna, three if the feed network is disposed on the back side (not shown).
FIG. 2 is a front perspective view of another prior art antenna assembly. In FIG. 2 a slot resonator is cut into a conducting plane. This provides a single linear polarization in the transmitted signal (vertical as shown in FIG. 2). Two conductors are sufficient-ground and feed. This approach provides bidirectional radiation (upward and downward in the FIG. 2 view).
It would be desirable to be able to deploy an antenna assembly more suitable to the random polarizations expected from retail merchandise packed on shelves or other retail sales areas.